Sea urchins from the phylum Echinodermata are formed with a domed back side generally referred to as the posterior side and a flattened mouth side generally referred to as the anterior side. The sea urchin has spines covering all of its shell. However the spines are shorter and more uniform in size on the mouth side. A variety of sea urchin species share these characteristics.
Green sea urchins are generally found in latitudes above 40.degree. north and below 40.degree. south in all oceans. In North America they are commonly found from Atlantic Canada to Cape Cod on the Atlantic coast and from the Aleutian Islands to British Columbia on the Pacific Coast. The commercial size of green sea urchins generally ranges from 11/2 to 41/2 inches (3.8 to 11.4 cm) in diameter with spine lengths up to 1/2 an inch (1.3 cm).
Red sea urchins are commonly found from Juneau, Alaska to Mexico on the Pacific Coast. Red sea urchins are roughly double the size of the green sea urchin varieties and have longer spines, for example up to several inches (7.6 cm) in length.
Purple sea urchins occur in the region of overlap of red and green sea urchins on the Pacific Coast. Purple sea urchins are approximately the same size as the green sea urchins.
The traditional procedure for opening sea urchins to extract the gonad lobes is to use a hand held shell cracking tool. This tool is inserted into the mouth end of the sea urchin shell. The two halves of the tool are forced apart splitting open the shell. A similar cracking mechanism for cracking open the shells of sea urchins is described for example in the O'Donnell U.S. Pat. No. 4,393,545 issued in 1983 for "Processing of Sea Urchins".
Several problems occur according to the traditional procedure using such cracking tools. First, one or more of the sea urchin gonad lobes are generally broken in the process of cracking open the sea urchin shell. Second the gonad lobes are separated from the integral star shaped ring into separate lobes. Finally shell bits are occasionally driven into the gonad lobes and must be removed using tweezers. No mechanization of the traditional procedure has successfully resolved these problems.